(1) Field of the Invention
The present invention relates to a solid-state imaging device in which plural photo-electric converters are allocated in an array shape, and to a driving method and a manufacturing method thereof.
(2) Description of the Related Art
In recent years, the demand for miniaturization of MOS-type solid-state imaging devices has increased. On the other hand, improvements in image quality are also required, and increasing the amount of saturated electrons in photodiode (PD) units, i.e. photo-electric converters, is necessary. Also, when the number of saturated electrons is increased, read defects may easily occur, resulting in an after-image defect. Therefore, it is necessary to increase the capacity of photodiodes and completely transfer charge that is accumulated in a photodiode.
A method used to boost the gate voltage more than the power voltage has been proposed in order to increase the capacity of the photodiode of the solid-state imaging device and completely transfer the charge in the photodiode of the solid-state imaging device.
The conventional solid-state imaging device is designed to improve read-out properties by decreasing the electron potential of the charge transfer circuit below the gate, thereby increasing the gate voltage more than the power voltage in the boost circuit. For example, in Non-Patent Reference 1, 1.32 times 3.3V is studied as a gate voltage for improving the read-out properties compared to a power source voltage of 2.5 V. The general degree of modulation in the transfer transistor is from 0.65 to 0.75, for example, and when the potential in the gate electrode is 3.3V, the potential of the charge transfer path below the gate is between 2.14 and 2.475V. Here, a signal charge may flow from the charge transfer path to the FD unit, since the potential of the charge transfer path below the gate decreases to less than the potential of the FD unit.
[Non-patent Reference 1] IEDM2005 Digest 33-2 “The features and characteristics of 5M CMOS image sensor with 1.9×1.9 μm2 pixels” 2005 IEEE